Matthias Henker

The digital front-end of software radio terminals

When expanding digital signal processing of mobile communications terminals toward the antenna while making the terminal more wideband in order to be able to cope with different mobile communications standards in a software radio based terminal, the designer is faced with strong requirements such as bandwidth and dynamic range. Many publications claim that only reconfigurable hardware such as FPGAs can simultaneously cope with such diversity and requirements. Starting with considerations of the receiver architecture, we describe key functionalities of the digital front-end and highlight how the signal characteristics of mobile communications signals and commonalities among different signal processing operations can be exploited to great advantage, eventually enabling implementations on an ASIC that, although not reconfigurable, would empower the software radio concept.

Time-variant CIC-filters for sample rate conversion with arbitrary rational factors

Sample rate conversion (SRC) with rational factors can be realized by interpolation followed by decimation, where CIC-filters can be chosen for either. However, the necessary increase of the sample rate that goes with the interpolation is not feasible in most RF applications. Therefore a time-variant implementation of CIC-filters is presented which circumvents the high intermediate sample rate. This time-variant implementation results in a linear periodically time-variant system (LPTV) which is completely equivalent to its original linear time-invariant system (LTI) consisting of the interpolator and the decimator. Thus well-known methods of system analysis can be used by analysing the LTI system, while implementing the system as an LPTV system, avoiding the high intermediate sample rates of the LTI system. The advantage of CIC-filters not having stored the coefficients of the impulse response but rather the description of the impulse response, enabling an implementation which is independent of the interpolation- as well as the decimation-factor, is preserved with the LPTV system. In contrast to Lagrange interpolators cancelling only the image components of the interpolated signal, time-variant CIC-filters also cancel the aliasing components, which is important in applications, where antialiasing is more important than anti-imaging.

Hardware in a loop-a system prototyping platform for MIMO-approaches

The hardware in a loop concept is introduced for the design of wireless communication chipsets. The aim is to verify the algorithm design followed by extensive software simulations of the proposed algorithms. Signalion provides a rapid prototyping platform to enable this algorithm verification on a hardware. This approach helps to identify design errors and implementation faults. The hardware platform can be used for complex PHY implementations such as MIMO-OFDM modems.